[freetype2] hdmx-advances b00ee99: [truetype] Binary search through `hdmx` records.

[Werner Lemberg]

branch: hdmx-advances
commit b00ee992abea270850733fb312c7b1bf4428c080
Author: Alexei Podtelezhnikov <apodtele@gmail.com>
Commit: Alexei Podtelezhnikov <apodtele@gmail.com>

    [truetype] Binary search through `hdmx` records.
    
    The `hdmx` table is supposed to be sorted by ppem size, which
    enables binary search.  We also drop the check for the sufficient
    length of the record because it is now enforced when the table
    is loaded.
    
    * src/truetype/ttpload.c (tt_face_load_hdmx): Prudently sort records.
    (tt_face_get_device_metrics): Implement binary search to retrieve
    advances.
---
 src/truetype/ttpload.c | 37 ++++++++++++++++++++++++++++---------
 1 file changed, 28 insertions(+), 9 deletions(-)

diff --git a/src/truetype/ttpload.c b/src/truetype/ttpload.c
index 71db75a..44b5dae 100644
--- a/src/truetype/ttpload.c
+++ b/src/truetype/ttpload.c
@@ -498,6 +498,14 @@
   }
 
 
+  FT_COMPARE_DEF( int )
+  compare_ppem( const void*  a,
+                const void*  b )
+  {
+    return *(FT_Byte*)a - *(FT_Byte*)b;
+  }
+
+
   /**************************************************************************
    *
    * @Function:
@@ -577,8 +585,10 @@
     if ( FT_QNEW_ARRAY( face->hdmx_record_sizes, num_records ) )
       goto Fail;
 
-    /* XXX: We do not check if the records are sorted by ppem */
-    /* and cannot use binary search later.                    */
+    /* The records must be already sorted by ppem but it does not */
+    /* hurt to make sure so that the binary search works later.   */
+    ft_qsort( p, num_records, record_size, compare_ppem );
+
     for ( nn = 0; nn < num_records; nn++ )
     {
       if ( p + record_size > limit )
@@ -619,27 +629,36 @@
   /**************************************************************************
    *
    * Return the advance width table for a given pixel size if it is found
-   * in the font's `hdmx' table (if any).
+   * in the font's `hdmx' table (if any).  The records must be sorted for
+   * the binary search to work properly.
    */
   FT_LOCAL_DEF( FT_Byte* )
   tt_face_get_device_metrics( TT_Face  face,
                               FT_UInt  ppem,
                               FT_UInt  gindex )
   {
-    FT_UInt   nn;
+    FT_UInt   min         = 0;
+    FT_UInt   max         = face->hdmx_record_count - 1;
+    FT_UInt   mid;
     FT_Byte*  result      = NULL;
     FT_ULong  record_size = face->hdmx_record_size;
     FT_Byte*  record      = FT_OFFSET( face->hdmx_table, 8 );
 
 
-    for ( nn = 0; nn < face->hdmx_record_count; nn++ )
-      if ( face->hdmx_record_sizes[nn] == ppem )
+    do
+    {
+      mid = ( min + max ) >> 1;
+
+      if ( face->hdmx_record_sizes[mid] > ppem )
+        max = mid - 1;
+      else if ( face->hdmx_record_sizes[mid] < ppem )
+        min = mid + 1;
+      else
       {
-        gindex += 2;
-        if ( gindex < record_size )
-          result = record + nn * record_size + gindex;
+        result = record + mid * record_size + gindex + 2;
         break;
       }
+    } while ( max >= min );
 
     return result;
   }